Conductive articles and processes for their preparation

ABSTRACT

Articles are disclosed in which an electrically conductive layer on a substrate exhibits a superconducting transition temperature in excess of 30° K. Conductive layers are disclosed comprised of a crystalline rare earth alkaline earth copper oxide. Processes of preparing these articles are disclosed in which a mixed metal oxide precursor composition is coated and heated to its thermal decomposition temperature to create an amorphous mixed metal oxide layer. The amorphous layer is then heated to its crystallization temperature.

This is a division of U.S. Pat. Ser. No. 046,593, filed May 4, 1987, nowU.S. Pat. No. 4,880,770, issued Nov. 14, 1989.

FIELD OF THE INVENTION

The present invention relates to articles having conductive coatings, toprocesses for preparing these articles, and to useful intermediatearticles. In certain preferred forms this invention relates to articleshaving superconductive coatings and processes for their preparation.

BACKGROUND OF THE INVENTION

The term "superconductivity" is applied to the phenomenon ofimmeasurably low electrical resistance exhibited by materials. Untilrecently superconductivity had been reproducibly demonstrated only attemperatures near absolute zero. As a material capable of exhibitingsuperconductivity is cooled, a temperature is reached at whichresistivity decreases (conductivity increases) markedly as a function offurther decrease in temperature. This is referred to as thesuperconducting transition temperature or, in the context ofsuperconductivity investigations, simply as the critical temperature(T_(c)). T_(c) provides a conveniently identified and generally acceptedreference point for marking the onset of superconductivity and providingtemperature rankings of superconductivity in differing materials.

It has been recently recognized that certain rare earth alkaline earthcopper oxides exhibit superconducting transition temperatures well inexcess of the highest previously known metal oxide T_(c), a 13.7° K.T_(c) reported for lithium titanium oxide. These rare earth alkalineearth copper oxides also exhibit superconducting transition temperatureswell in excess of the highest previously accepted reproducible T_(c),23.3° K. for the metal Nb₃ Ge.

Recent discoveries of higher superconducting transition temperatures inrare earth alkaline earth copper oxides are reported in the followingpublications:

P-1 J.G. Bednorz and K.A. Muller, "Possible High T_(c) Superconductivityin the Ba--La--Cu--O-- System", Z. Phys. B. Condensed Matter. Vol. 64,pp. 189-193 (1986) revealed that polycrystalline compositions of theformula Ba_(x) La_(5-x) Cu₅ O₅(3-y), where x=1 and 0.75 and y>0 exhibitsuperconducting transition temperatures in the 30° K. range.

P-2 C.W. Chu, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, and Y.Q. Wang,"Evidence for Superconductivity above 40 K in the La--Ba--Cu--O--Compound System", Physical Review Letters, Vol. 53. No. 4. pp. 405-407.Jan. 1987, reported increasing T_(c) to 40.2° K. at a pressure of 13kbar. At the end of this article it is stated that M.K. Wu increasedT_(c) to 42° K. at ambient pressure by replacing Ba with Sr.

P-3 C.W. Chu, P.H. Hor, R.L. Meng, L. Gao, and Z J. Huang,"Superconductivity at 52.5 K in the Lanthanum Barium Copper OxideSystem", Science Reports, Vol. 235, pp. 567-569, Jan. 1987, a T_(c) of52.5° K. for (La₀.9 Ba₀.1)₂ CuO_(4-y) at high pressures.

P-4 R.J. Cava, R.B. vanDover, B. Batlog, and E.A. Rietman, "BulkSuperconductivity at 36 K in La₁.8 Sr₀.2 CuO₄ ", Physical ReviewLetters, Vol. 58, No. 4, pp. 408-410, Jan. 1987. reported resistivityand magnetic susceptibility measurements in La_(2-x) Sr_(x) CuO₄, with aT_(c) at 36.2° K. when x=0.2.

P-5 J.M. Tarascon, L.H. Greene, W.R. McKinnon, G.W. Hull, and T.H.Geballe, "Superconductivity at 40 K in the Oxygen Defect PerovskitesLa_(2-x) Sr_(x) CuO_(4-y) ", Science Reports, Vol. 235, pp. 1373-1376.Mar. 13. 1987. reported title compounds (0.05≦x≦1.1) with a maximumT_(c) of 39.3° K.

P-6 M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J.Huang, Y.Q. Wang, and C.W. Chu, "Superconductivity at 93 K in a NewMixed Phase Y--Ba--Cu--O Compound System at Ambient Pressure", PhysicalReview Letters, Vol. 58, No. 9, pp. 908-910, Mar. 2, 1987, reportedstable and reproducible superconducting transition temperatures between80 and 93° K. at ambient pressures for materials generically representedby the formula (L_(1-x) M_(x))_(a) A_(b) D_(y), where L═Y, M═Ba, A═Cu,D═O, x═0.4, a═2, b═1, and y═4.

The experimental details provided in publications P-1 through P-6indicate that the rare earth alkaline earth copper oxides prepared andinvestigated were in the form of cylindrical pellets produced by formingan amorphous oxide by firing, grinding or otherwise pulverizing theamorphous oxide, compressing the particulate amorphous oxide formed intocylindrical pellets, and then sintering to produce a polycrystallinepellet. While cylindrical pellets are convenient articles for coolingand applying resistance measuring electrodes, both the pellets and theirpreparation procedure offer significant disadvantages to producinguseful electrically conductive articles, particularly articles whichexhibit high conductivity below ambient temperature--e.g.,superconducting articles. First. the step of grinding or pulverizing theamorphous oxide on a commercial scale prior to sintering is both timeand energy consuming and inherently susceptible to material degradationdue to physical stress on the material itself, erosion of grindingmachinery metal. and handling. Second, electrically conductive articlesrarely take the form of pellets. Electrically conductive articles mostcommonly take the form of flexible elongated conductive articles--e.g.,wires, and articles forming conductive pathways on a substrate, such asinsulative and semiconductive substrates--e.g , printed and integratedcircuits.

SUMMARY OF THE INVENTION

In one aspect this invention is directed to an article comprised of asubstrate and an electrically conductive layer located on the substratecharacterized in that the electrically conductive layer is comprised ofa crystalline rare earth alkaline earth copper oxide.

In another aspect this invention is directed to an electricallyconductive article comprised of a substrate and at least oneelectrically conductive layer characterized in that the conductive layerexhibits a superconducting transition temperature of at least 30° K.

In an additional aspect this invention is directed to an electricallyconductive article comprised of a substrate and at least oneelectrically conductive layer characterized in that the conductive layerexhibits superconductivity at temperatures in excess of 10° K.

In still another aspect this invention is directed to an articlecomprised of a substrate and a layer of an amorphous metal oxide locatedon the substrate characterized in that the amorphous metal oxide is arare earth alkaline earth copper oxide.

In still an additional aspect this invention is directed to a processcomprising applying to a substrate metal oxide precursors and thermallydecomposing the precursors. The process is characterized in that ontothe substrate is coated a solution consisting essentially of avolatilizable film forming solvent and metal ligand compounds of each ofrare earth, alkaline earth, and copper containing at least one thermallyvolatilizable ligand and the solvent and ligands are removed from thesubstrate, this step including heating in the presence of oxygen to forman amorphous rare earth alkaline earth copper oxide coating on thesubstrate.

In a more specific aspect this invention is directed to a process offorming a pattern of crystalline rare earth alkaline earth copper oxideon a substrate. The process comprises (a) coating onto the substrate asolution consisting essentially of a volatilizable film forming solventand metal ligand compounds of each of rare earth, alkaline earth, andcopper containing at least one thermally volatilizable ligand, (b)removing the solvent and ligands from the substrate, this step includingheating in the presence of oxygen to form an amorphous rare earthalkaline earth copper oxide coating on the substrate, (c) forming aphotoresist pattern on the amorphous coating, (d) removing the amorphouscoating not protected by the photoresist pattern, (e) removing thephotoresist pattern, and (f) converting the amorphous rare earthalkaline earth copper oxide remaining on the substrate to a crystallinecoating by heating the amorphous coating to a temperature at whichcrystallization of the rare earth alkaline earth copper oxide occurs.

In another specific aspect this invention is directed to a process ofproducing a flexible elongated electrical conductor comprisingtransporting a flexible elongated substrate through a coating zone whereit is coated with a precursor of an electrical conductor andtransporting the substrate from the coating zone into a heating zone toconvert the precursor to an electrically conductive form. The process ischaracterized in that (a) in the coating zone the substrate is broughtinto contact with a solution consisting essentially of a volatilizablefilm forming solvent and metal ligand compounds of each of rare earth,alkaline earth, and copper containing at least one thermallyvolatilizable ligand, (b) in a first region of the heating zone thesolvent and ligands are removed from the substrate. this step includingheating in the presence of oxygen to form an amorphous rare earthalkaline earth copper oxide coating on the substrate, and (c) in asecond region of the heating zone the amorphous rare earth alkalineearth copper oxide is converted to an electrically conductive form byheating the amorphous oxide to a temperature at which crystallization ofthe rare earth alkaline earth copper oxide occurs.

The present invention makes available to the art for the first timearticles containing an electrically conductive rare earth alkaline earthcopper oxide layer. In addition the present invention makes available tothe art for the first time an electrically conductive article providinga coating on a support having a superconducting transition temperaturein excess of 30° K. Further, these articles are capable of beingfabricated in any of the most commonly employed geometrical forms ofelectrically conductive elements. This invention makes possibleelectrically conductive elongated articles, such as elongated flexiblearticles employed for the fabrication of leads and windings inelectrical circuits as well as electrically conductive articlesexhibiting circuit patterns--e.g., printed, hybrid, and integratedcircuits. The present invention also makes available to the art uniquethin film elements.

Additionally the present invention makes available to the artintermediate articles which can be further fabricated by subsequentfabricators to satisfy specific circuit applications. That is, thepresent invention makes available intermediate articles which can beprocessed further to produce desired circuitry.

The articles of this invention can be fabricated by techniques thatavoid the disadvantages of the prior art. No grinding or pulverizingsteps are required. In addition, the fabrication processes of thisinvention lend themselves to fabrication of articles of the mostcommonly employed electrical conductor geometrical forms. Specificprocesses of the invention allow conductive layer patterning. Further,conductive layers and pathways can be formed in the articles of theinvention with minimal heating of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the invention can be better appreciated byreference to the following detailed description of preferred embodimentsconsidered in conjunction with the drawings, in which

FIG. 1 is schematic diagram showing process steps and articles producedthereby;

FIG. 2 is a schematic diagram of an arrangement for coating a elongatedflexible substrate;

FIG. 3 is a schematic diagram of process steps and articles formedthereby capable of forming a patterned conductor on a substrate and

FIGS. 4 through 8 are plots of temperature in degrees Kelvin versusresistance, measured in ohms or kilo-ohms, as indicated.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention has as its purpose to make available electricallyconductive articles exhibiting a rare earth alkaline earth copper oxideconductive layer coated on a substrate. The term "rare earth alkalineearth copper oxide" refers to a composition of matter containing atleast one rare earth element, at least one alkaline earth element,cooper, and oxygen. The term "rare earth" is employed to designateyttrium and lanthanides--i.e., elements of the lanthanide series.Lanthanum, samarium, europium, gadolinium, dysprosium, holmium, erbium,and ytterbium are particularly preferred lanthanides. The term "alkalineearth" indicates elements of Group 2 of the Periodic Table of elementsas adopted by the American Chemical Society. Calcium, strontium andbarium are preferred alkaline earth elements for the practice of thisinvention.

In keeping with the established practice in the ceramics art ofshortening lengthy chemical names of mixed metal oxides by substitutingacronyms based on the first letters of the metals present, the term"RAC" is hereinafter employed to indicate generically rare earthalkaline earth copper oxides. When it is intended to designatespecifically a lanthanide or yttrium as the rare earth component, L orY, respectively, is substituted for R., and when it is intended todesignate specifically strontium or barium as the alkaline earthcomponent, S or B, respectively, is substituted for A.

Except as otherwise noted, all steps in the preparation of electricallyconductive articles according to this invention are understood to bepracticable in air at atmospheric pressure. It is, of course, recognizedthat increasing the proportion of ambient oxygen present and operationat elevated pressures, used separately or together, is generallycompatible with the practice of this invention and can be employed,although not required.

The present invention can be appreciated by the schematic diagram shownin FIG. 1. In Step A of the preparation process, onto a substrate iscoated a solution consisting essentially of a volatilizable film formingsolvent and metal ligand compounds of each of rare earth, alkalineearth, and copper containing at least one thermally volatilizableligand. The resulting coated article 1 as schematically shown consistsof substrate 3 and a layer 5 formed by RAC precursors (metal.-ligandcompounds) and film forming solvent.

In Step B article 1 is heated to a temperature sufficient to volatilizethe ligands and the film forming solvent. The element 7 resultingconsists of substrate 3 and amorphous RAC layer 9. In its amorphous formthe RAC coating exhibits relatively low levels of electricalconductivity.

To convert the amorphous RAC layer to a more highly conductive form itis necessary to induce crystallization of the RAC layer. In Step C thearticle 7 is heated to a temperature sufficient to convert the amorphousRAC layer to a more electrically conductive crystalline form. In article11 the RAC layer 13 on substrate 3 is crystalline.

Crystallization of the RAC layer occurs in two stages--crystalnucleation and crystal growth. It is in some instances preferred toachieve crystal nucleation at a somewhat different temperature than isemployed for crystal growth. Microscopic examination of articles at anearly stage of crystallization reveals crystal nuclei surrounded by atleast one other RAC phase. Further heating of the RAC layer at thetemperature of nucleation or, preferably, at a somewhat highertemperature increases the size of the crystal nuclei at the expense ofthe surrounding RAC phase or phases until facets of adjacent crystalsare grown into electrically conductive juxtaposition.

According to accepted percolation theory, for a layer consisting ofconducting spheres located in a surrounding nonconducting medium thespheres must account for at least 45 percent by volume of the layer forsatisfactory electrical conductivity to be realized. If conductingparticles of other geometric forms, particularly elongated forms, aresubstituted for the spheres, the conducting particles can account forless of the layer volume while still realizing satisfactory layerelectrical conductivity. Similarly, electrical conductivity can berealized with a lesser proportion of conducting particles when thesurrounding medium is also conductive. Thus, all layers containing atleast 45 percent by volume electrically conductive particles are bytheory electrically conductive.

Although satisfactory electrical conductivity can be realized with alesser volume of the crystalline phase, it is generally contemplatedthat in the crystallized RAC layer the crystalline phase will accountfor at least 45 percent by volume and preferably 70 percent by volume ofthe total RAC layer. From microscopic examination of highly crystallineRAC layers exhibiting high levels of electrical conductivity it has beenobserved that layers can be formed in which little, if any, of the RACphase surrounding the crystal nuclei remains. In other words greaterthan 90 percent (and in many instances greater than 99 percent) byvolume of the RAC layer is accounted for by the desired crystallinephase.

To achieve crystallization the RAC layer can be heated to any convenienttemperature level. To avoid interaction with less than inert substrates,it is generally preferred that heating of the RAC layer be heated nohigher than is required for satisfactory crystallization. Heating toachieve crystallization can, for example, be limited to temperaturesbelow the melting point of the RAC composition forming the layer.Microscopic examination of coatings of some RAC compositions hasrevealed that extending heating temperatures or times beyond thoseproducing crystallization can result in rounding of crystal corners andedges. It is believed that the rounding resulting from further heatingreduces the area of contact between adjacent crystal facets and thusrestricts the conduction path through the crystalline RAC layer. Frommicroscopic examination of RAC layers optimum heating times can beselected for maximizing both the proportion of the RAC layer accountedfor by the crystalline phase and the desired configuration of thecrystals produced, thereby maximizing electrical conductivity.

Step D entails controlled cooling of the RAC layer from itscrystallization temperature. By slowing the rate of cooling of thecrystalline RAC layer imperfections in the crystal lattices can bereduced and electrical conductivity, which is favored with increasingorder in the crystal structure, is increased. Cooling rates of 25° C.per minute or less are contemplated until the crystalline RAC layerreaches a temperature of at least 500° C. or, preferably, 200° C. Belowthese temperatures the lattice is sufficiently rigid that the desiredcrystal structure is well established. The article 15 produced is formedof the annealed crystalline RAC layer 17 on substrate 3.

While the article 15 exhibits high levels of electrical conductivity, insome instances further heating of the article 15 in an oxygen enrichedatmosphere has been observed to increase electrical conductivityfurther. In addition to oxygen supplied from the ligands the oxygenforming the crystalline RAC layer is obtained from the ambientatmosphere, typically air. It is believed that in some instances,depending upon the crystal structure being produced, ambient air doesnot provide the proportion of oxygen needed to satisfy entirely theavailable crystal lattice sites.

Therefore, optional Step E entails heating the article 15 in an oxygenenriched atmosphere, preferably pure oxygen. The object is toequilibrate the RAC crystalline layer with the oxygen enrichedatmosphere, thereby sufficient oxygen into the crystal latticestructure. Temperatures for oxygen enrichment of the crystalline RAClayer are above the minimum annealing temperatures employed in Step Ddescribed above. To be effective in introducing oxygen into the crystallattice temperatures above those at which the lattice becomes rigid arenecessary. The duration and temperature of heating are interrelated,with higher temperatures allowing shorter oxygen enrichment times to beemployed. Substantially complete oxygen equilibration can be realized atnear minimum temperatures in about 1 hour.

In preparing RAC layers shown to be benefitted by oxygen enrichment ofthe ambient atmosphere Step E can be consolidated with either or both ofSteps C and D. Oxygen enrichment is particularly compatible with Step D,allowing annealing out of crystal lattice defects and correction ofcrystal lattice oxygen deficiencies to proceed concurrently.

The final electrically conductive article 19 is comprised of acrystalline, electrically conductive RAC layer 21 on substrate 3.Depending upon specific choices of materials and preparation techniques,the article 19 can exhibit a high superconducting transitiontemperature, herein employed to designate a T_(c) of greater than 30° C.

The process described for preparing electrically conductive articleshaving RAC layers offers several distinct advantages. One of the mostsignificant advantages is that the proportions of rare earth, alkalineearth, and copper elements in the final RAC layer 21 exactly correspondto those present in the RAC precursor layer 5. In other words, the finalproportion of rare earth, alkaline earth, and copper elements isdetermined merely by mixing in the desired proportions in the filmforming solvent the metal ligand compounds employed as startingmaterials. This avoids what can be tedious and extended trial and erroradjustments of proportions required by commonly employed metal oxidedeposition techniques, such as sputtering and vacuum vapor deposition.Further, the present process does not require any reduction ofatmospheric pressures, and thus no equipment for producing either highor low vacuum.

A further significant advantage of the process of this invention is thatit can be applied to the fabrication of electrically conductive articlesof varied geometry, particularly those geometrical forms of electricalconductors most commonly employed.

The present invention lends itself readily to the preparation ofelongated electrically conductive articles, particularly flexibleelongated electrically conductive articles, such as those employed aselectrical leads, conductive windings in electro-magnets, conductivearmature and/or field windings in electrical motors and generators,conductive windings in transformers, conductive windings in solenoids,and as long distance electrical transmission lines. Contemplatedflexible elongated electrically conductive articles include thosereferred to in the art as rods, wires, fibers, filaments, threads,strands, and the like. In addition conductive cladding of ribbons,sheets, foils, and films is contemplated.

A coating process particularly adapted to coating flexible substratescan be illustrated by reference to FIG. 2, wherein an elongated flexiblesubstrate 25 is unwound from a supply spool 27 and passed downwardlyover a guide roller 29 into a reservoir 31. The reservoir contains afilm forming solvent with metal ligand compounds dissolved therein, asdescribed above in connection with Step A, shown as a liquid body 33.The flexible substrate is drawn over a lower guide roller 35 whileimmersed in the liquid and then passed upwardly to a third guide roller37.

As the flexible substrate is drawn upwardly it emerges from the liquidbody bearing an annular thin, uniform surface layer corresponding tolayer 5 in FIG. 1. Between the reservoir and the third guide roller thecoated substrate is drawn through a heating zone to complete indifferent regions of the heating zone process Steps B, C, D, and Esequentially as previously described. To accommodate needs for differentresidence times within the various heating regions the lengths of thedifferent regions can be adjusted. Additionally, residence time of asubstrate within any heating region can be further increased byemploying laterally diverting guides, so one or a number of coatedsubstrate festoon like path diversions are created within the heatingregion.

After passing over the third guide roller the substrate, bearing anannular crystalline electrically conductive RAC layer is wound onto astorage spool 39. Where the RAC layer is coated on a flexible substrate,it is preferred to maintain the thickness of the RAC layer at 2 μm orless, preferably 1.0 μm or less, so that it exhibits adequateflexibility. Flexing of the RAC layer required by guiding and spoolingby can be reduced by increasing the radius of curvature imposed by thethird guide roller and storage spool.

The arrangement shown in FIG. 2 for applying a flexible RAC layer to aflexible substrate is, of course, merely illustrative of a number ofapproaches which can be employed to apply a RAC layer to a flexiblesubstrate. Where it is more convenient to perform process steps B, C, D,and E in a horizontally offset rather than vertically offset spatialrelationship, instead of applying the RAC precursors and film formingsolvent by immersion of the substrate, other conventional coatingapproaches can be employed for application, such as roll coating,spraying, brushing, curtain coating, extrusion, or the like. It isgenerally preferred to avoid guide contact of the coated substratebetween application of the RAC precursors and completion of Step B.However, once a solid RAC layer exists on the substrate, guide contactwith the substrate within or between any one of process Step C, D, and Elocations can be undertaken, as desired for convenient spatialorientation.

While flexible electrical conductors of extended length serve a varietyof important applications, there are many other applications forelectrical conductors, particularly those located on limited portions ofsubstantially planar surfaces of substrates. Such applications includethose served by conventional printed, integrated, and hybrid circuits.In such circuits limited, if any, flexibility of the electricalconductor is required, but an ability to define areally--i.e, pattern,the electrical conductor with a high degree of precision is in manyinstances of the utmost importance. The present invention is compatiblewith precise patterning of the electrical conductor on a substratesurface.

Patterning of an electrical conductor according to this invention isillustrated by reference to FIG. 3. Substrate 3 is coated on its upperplanar surface with a uniform RAC precursor layer 5 as described abovein connection with process Step A to form initial coated article 1.Process Step B, described above, is performed on article 1 to producearticle 7, described above, comprised of amorphous RAC layer 9 andsubstrate 3.

The amorphous RAC layer lends itself to precise pattern definition andproduces results generally superior to those achieved by patterning theRAC precursor layer from which it is formed or the crystalline RAC layerwhich is produced by further processing. The RAC precursor layer isoften liquid before performing process Step B and is in all instancessofter and more easily damaged in handling than the amorphous RAC layer.The crystalline RAC layer cannot be etched with the same boundaryprecision as the amorphous RAC layer, since etch rates vary from pointto point based on local variations in the crystal faces and boundariespresented to the etchant. Patterning of either the RAC precursor layeror the crystalline RAC layer is specifically recognized as a viablealternative to patterning the amorphous RAC layer for applicationspermitting more tolerance of conductor dimensions. For example, screenprinting the RAC precursor layer on a substrate to form a printedcircuit is specifically contemplated.

While the amorphous RAC layer can be patterned employing anyconventional approach for patterning metal oxides, for more precise edgedefinitions the preferred approach is to photopattern the amorphous RAClayer employing any of the photoresist compositions conventionallyemployed for the precise definition of printed circuit or integratedcircuit conductive layers. In a preferred form of the process, a uniformphotoresist layer 23 is applied to the amorphous RAC layer 9 asindicated by process Step B-1. The photoresist layer can be formed byapplying a liquid photoresist composition to the substrate, spinning thesubstrate to insure uniformity of the coating, and drying thephotoresist. Another approach is to laminate a preformed photoresistlayer supported on a transparent film to the amorphous RAC layer.

The photoresist layer is then imagewise exposed to radiation, usuallythrough a mask. The photoresist can then be removed selectively as afunction of exposure by development. Positive working photoresists areremoved on development from areas which are exposed to imaging radiationwhile negative working photoresists are removed only in areas which arenot exposed to imaging radiation. Exposure and development are indicatedby process Step B-2. Following this step patterned photoresist layer 23ais left on a portion or portions of the amorphous RAC layer 9. Althoughthe patterned residual photoresist layer is for convenience shown of asimple geometrical form, it is appreciated that in practice thepatterned photoresist can take any of a wide variety of geometricalforms, including intricate and thin line width patterns, with linewidths ranging into the sub micrometer range.

Following patterning of the photoresist layer, portions of the RAC layerwhich are not protected by the photoresist can be selectively removed byetching, as indicated by process Step B-3. This converts the amorphousRAC layer 9 to a patterned RAC layer 9a confined to areas correspondingto that of the photoresist.

Following patterning of the amorphous RAC layer the patternedphotoresist is removed, as indicated by process Step B-4. The finalarticle as shown in FIG. 3 consisting of the substrate 3 and patternedamorphous RAC layer 9a is then further processed as indicated in FIG. 1,picking up with process Step C. The crystalline RAC layer formed in thefinal product conforms to the patterned amorphous RAC layer.

In the process of preparing a patterned article described above it isnoted that once an article is formed having an amorphous RAC layer on asubstrate it can be patterned to serve any of a wide variety of circuitapplications, depending upon the circuit pattern chosen. It is thereforerecognized that instead of or as an alternative to offering patternedarticles for sale a manufacturer can instead elect to sell articles withunpatterned amorphous RAC layers, with or without an unpatternedphotoresist layer, to subsequent fabricators. It will often beconvenient in this instance to locate a removable layer or film over theamorphous RAC layer for its Protection prior to further fabrication. Thesubsequent fabricator can undertake the patterned exposure and furtherprocessing required to produce a finished electrically conductivearticle.

To crystallize a RAC layer and to perform the optional, but preferredannealing and oxygen enrichment steps both the substrate and RAC layerare heated uniformly. This can be done employing any conventional oven.In some instances, however, either to protect the substrate from risingto the peak temperatures encountered by the RAC layer or simply to avoidthe investment in an oven by fabricator, it is contemplated that the RAClayer will be selectively heated. This can be accomplished by employinga radiant heat source, such as a lamp--e.g., a quartz lamp. Lamps ofthis type are commercially available for achieving rapid thermalannealing of various conventional layers and can be readily applied tothe practice of the invention. These lamps rapidly transmit high levelsof electromagnetic energy to the RAC layer, allowing it to be brought toits crystallization temperature without placing the substrate in anoven.

A diverse approach for producing patterned electrical conductors can bepracticed by employing article 7 comprised of the uniform amorphous RAClayer 9 and substrate 3 as a starting element. Instead of patterning theamorphous RAC layer followed by crystallization of the remainingportions of the layer, the amorphous RAC layer is imagewise addressed toproduce crystallization selectively only in areas intended to berendered electrically conductive. For example, by addressing theamorphous RAC layer with a laser areas directly impinged by the laserbeam can be selectively crystallized to an electrically conductive formleaving the remaining amorphous areas unaffected. To define theconductive pattern generated it is only necessary to control the path ofthe laser beam.

Where a manufacturer chooses to sell an article consisting of a uniformamorphous RAC layer on a substrate, this approach to patterning can bemore attractive than the uniform heating processes described above,since no oven is required to reach the temperatures typically requiredfor crystallization. The fabricator choosing laser patterning may, infact, require no other heating equipment. Thus, a very simple approachto forming a crystalline RAC pattern is available.

It is, of course, recognized that additional heating for purposes ofannealing or oxygen saturation can be undertaken, following lamp orlaser crystallization, by heating in any desired manner. One approach isto heat at least amorphous layer 9 of the article 7 to a temperatureabove its minimum annealing temperature and then laser address theheated article. This facilitates annealing and oxygen enrichment withoutrequiring uniformly heating the entire article to the significantlyhigher levels otherwise required for crystal nucleation and growth.

Another variation on the laser patterning approach is to follow thelaser responsible for crystallization with one or more passes from alower intensity laser beam to retard the rate of cooling and therebyenhance annealing. For example, a laser beam can be swept across an areaof the substrate surface to produce crystallization and then reduced inintensity or defocused and swept back across the same area to facilitateannealing. By defocusing the laser beam on subsequent passes over thesame area the laser energy is spread over a larger area so that themaximum effective temperature levels achieved are reduced. The advantageof employing one laser for multiple passes is that alignments of laserbeam paths are more easily realized. Additionally or alternatively, therapidity with which the laser is swept across the exposed area can beadjusted to control the temperature to which it heats the RAC layer.Other laser scanning variations are, of course, possible.

Both lamp heating and laser canning allow a broader range of substratesto be considered, particularly those which, though capable ofwithstanding ligand and solvent volatilization temperatures, aresusceptible to degradation at crystallization temperatures. By choosingwavelengths in spectral regions to which the amorphous RAC layer isopaque or at least highly absorbing, direct radiant heating of thesubstrate can be reduced or eliminated. In this instance the bulk of theradiation is intercepted in the RAC layer before it reaches thesubstrate. The substrate can also be protected from direct radiantheating by choosing a substrate composition that is transparent to orminimally absorptive of the laser radiation. Since lasers emit coherentelectromagnetic radiation of a single wavelength, high selectivity ofabsorption or transmission is much more readily achieved than whenabsorption or transmission must be averaged over a wavelength region ofthe spectrum.

In considering crystallization of a RAC layer by radiant energy to whichthe RAC layer is opaque or at least highly absorptive and employing asubstrate which is substantially transparent to the radiant energy,whether supplied from a lamp or laser, advantages can be realized bysupplying the radiant energy to the RAC layer through the substrate.Where a substantially transparent substrate is employed, little of theradiant energy is attenuated in traversing the substrate. The RAC layeradsorbs the radiant energy adjacent its interface with the substrate.Thus, crystallization of the RAC layer can be initiated at thisinterface. By choosing a substrate of a crystal structure compatiblewith that of the crystals to be formed in the RAC layer, crystal growthin the RAC layer can occur epitaxially at the interface of the RAC layerand the substrate. In one form the substrate can be of the samecrystalline form sought in the RAC layer--e.g., a tetragonal K₂ NiF₄ orR₁ A₂ C₃ crystalline form. However, it is not essential that thesubstrate have the same crystal structure as the RAC layer for epitaxialdeposition to occur. What is most important is that the substratepresent a surface for deposition of the RAC layer that at leastapproximates the spatial frequency of atoms favorable for epitaxy. Forexample, it is possible to slice a monocrystalline substrate so that itpresents a planar surface having a frequency and spacing of oxygen atomsapproximating that in the desired crystalline phase of the RAC layer.The spatial frequency of oxygen atoms at the surface of the substratecan be chosen to match or approximate that of a tetragonal K₂ NiF₄ or R₁A₂ C₃ crystalline form, for instance, even though the substrate takes adifferent crystalline form.

To avoid coating imperfections the thickness of an amorphous RAC layerproduced in a single process sequence is maintained at 1 μm or less,preferably 0.6 μm or less, and optimally 0.4 μm or less, a singleprocess sequence being understood to constitute the steps describedabove for forming an amorphous RAC layer. By repeating the processsequence one or more times an amorphous RAC layer of any desiredthickness can be built up.

While ideal substrates are those which remain chemically nonreactiveduring fabrication of the crystalline RAC layer, in practice when RACcrystallization temperatures are encountered by the substrate at leastsome interaction of the RAC layer occurs with all but the most stable ofsubstrates. In some instances less than hoped for levels of electricalconductivity have been observed, believed to be attributable tointeraction of the crystallized RAC layer with its substrate at theirmutual interface. Unwanted reductions in T_(c) and zero resistivitytemperatures are believed to be unwanted manifestations of substrateinteraction with the crystalline RAC layer.

To minimize unwanted interaction of the RAC layer with the substrate itis specifically contemplated to interpose a barrier between thesubstrate and the RAC layer. It has been observed that each time the theprocess sequence required for forming the amorphous RAC layer isrepeated before proceeding on to the crystallization step of the processsubstrate interaction with the crystalline RAC layer is reduced, asreflected in its electrical conductivity properties, even wheremicroscopic examination reveals individual grains or microcrystalsextending from at or near the substrate to the top of the RAC layer. Inthis instance the portion of the crystalline RAC layer adjacent thesubstrate is acting as a barrier protecting the portion of the RAC layerremote from the substrate.

An alternative is to interpose between the substrate and the crystallineRAC layer a barrier of a different composition. The interposed barrierlayer can itself take the form of a crystalline RAC layer, differing inthe specific RAC composition chosen. In this instance the barrier layercan be viewed as a second crystalline RAC layer, which can, if desired,perform electrical conduction as well as acting as a barrier. In otherinstances the barrier can be viewed as an extension of the substrate.For example, a ceramic substrate coated with a thin refractory metallayer or a semiconductor substrate coated with an oxide or nitride, eachof which are in turn overcoated with a crystalline RAC layer, can beviewed as an article having a composite substrate supporting acrystalline RAC layer or an article having a unitary substrate, acrystalline RAC layer, and an interposed barrier.

Any rare earth alkaline earth copper oxide composition known to beconvertible to a crystalline phase can be employed in forming the coatedarticles of this invention. For example, any of the RAC compositionsdisclosed in publications P-1 through P-6 can be formed and converted toa crystalline phase by the process of this invention.

Further, electrically conductive crystalline RAC layers can be formed ona wide variety of substrates. In general any conventional electricalconductor substrate capable of withstanding processing temperatures canbe employed. For example, substrates in the form of metal wires, glassfibers, ceramic and glass plates, semiconductor wafers, and the like,all possess sufficient thermal stability to accept crystalline RAClayers applied by one or more of the procedures described above.

To achieve articles according to this invention which are not onlyelectrically conductive, but also exhibit high T_(c) levels, therebyrendering them attractive for high conductivity (e.g., superconducting)electrical applications, it has been observed that some combinations ofsubstrates and rare earth alkaline earth copper oxides are particularlyattractive in exhibiting higher T_(c) levels and higher maximumtemperatures at which superconductivity is in evidence.

One specifically preferred class of high T_(c) articles according tothis invention are those in which the crystalline RAC layer consists ofgreater than 45 percent by volume of a rare earth alkaline earth copperoxide which is in a tetragonal K₂ NiF₄ crystalline phase. The K₂ NiF₄crystalline phase preferably constitutes at least 70 percent andoptimally at least 90 percent by volume of the RAC layer.

A preferred rare earth alkaline earth copper oxide exhibiting thiscrystalline phase satisfies the metal ratio: (I)

    L.sub.2-x :M.sub.x :Cu

where

L is lanthanide,

M is alkaline earth metal and

x is 0.15 to 0.30.

Optimum results have been observed when x is 0.15 to 0.20 Among thepreferred lanthanides, indicated above, lanthanum has been particularlyinvestigated and found to have desirable properties. Preferred alkalineearth metals are barium and strontium. Optimum results have beenobserved when x is 0.15 to 0.20.

Thus, in specifically preferred forms of the invention LBC or LSC layersexhibiting a tetragonal K₂ NiF₄ crystalline phase are present andcapable of serving high conductivity applications, including thoserequiring high T_(c) levels and those requiring superconductivity attemperatures in excess of 10° K. Specific LBC layers in the tetragonalK₂ NiF₄ crystalline phase have been observed to have T_(c) levels inexcess of 40° K.

Another specifically preferred class of high T_(c) articles according tothis invention are those in which the crystalline RAC layer consists ofgreater than 45 percent by volume of a rare earth alkaline earth copperoxide which an R₁ A₂ C₃ crystalline phase, believed to be anorthorhombic Pmm2 or orthorhombically distorted perovskite crystalphase. This phase preferably constitutes at least 70 percent by volumeof the RAC layer.

A preferred rare earth alkaline earth copper oxide exhibiting thiscrystalline phase satisfies the metal ratio: (II)

    Y:M.sub.2 :Cu.sub.3

where

M is barium, optionally in combination with one or both of strontium andcalcium.

Although the R₁ A₂ C₃ crystalline phase by its crystal latticerequirements permits only a specific ratio of metals to be present, inpractice differing ratios of yttrium, alkaline earth, and copper arepermissible. The metal in excess of that required for the R₁ A₂ C₃crystalline phase is excluded from that phase, but remains in the YAClayer. This is further illustrated in the examples below.

As noted above, the formation of a particular crystalline orientation inthe RAC layer can be facilitated by employing a substrate which presentsa deposition surface of the same or a similar crystalline structure. Forexample, in seeking to form an oriented tetragonal K₂ NiF₄ crystallinephase in a RAC layer on a substrate it is most advantageous to employ asubstrate which at its interface with the RAC layer presents atetragonal K₂ NiF₄ crystal surface or a closely related crystalstructure, such as a perovskite.

It has been demonstrated that the R₁ A₂ C₃ crystalline phase can beformed on a perovskite crystal surface. High T_(c) articles consistingof LAC, particularly LSC, and YAC, particularly YBC, layers have beensuccessfully formed on substrates presenting a perovskite crystalsurface.

Alkaline earth oxides constitute a particularly preferred class ofsubstrates. They are in general relatively inert, refractory materialswhich exhibit limited interaction with the RAC layers during theirformation. Strontium titanate, because it can be readily formed in aperovskite crystalline form, constitutes a specifically preferredalkaline earth oxide substrate material. Although some interactionbetween alkaline earth oxide substrate and a contiguous RAC layer isbelieved to occur when the article is heated to temperatures above about900° C., interaction effects can be minimized by employing theinterposed barrier formation techniques, described above. It isgenerally preferred to perform the amorphous RAC layer formationprocessing sequence three to ten times to minimize substrate interactioneffects. Alumina and magnesia are other examples of specificallycontemplated oxide substrates.

To facilitate formation of the most highly uniform crystalline RAClayers it is preferred that the substrate itself be monocrystalline.Monocrystalline strontium titanate, alumina (sapphire) and magnesia(periclase) are all readily available substrate materials. Semiconductorwafers, particularly silicon and III-V compound wafers, also constituteuseful classes of monocrystalline substrates for the articles of thisinvention.

Another specifically contemplated class of substrate materials arerefractory metals. Such metals are, of course, well suited towithstanding RAC layer crystallization temperatures of 1000° C. or more.Refractory metals such as tungsten, tantalum, titanium, and zirconiumare particularly contemplated. The refractory metal can form the entiresubstrate or a thermally resistant layer onto which the RAC layer iscoated.

In the process of fabrication of this invention the formation of thedesired RAC layer begins with the formation of a RAC precursor layer,such as layer 5 in article 1, shown in FIG. 1. To form the precursorlayer a solution of a film forming solvent, a rare earth metal compound,an alkaline earth metal compound, and a copper compound is prepared.Each of the rare earth, alkaline earth, and copper compounds consists ofmetal ion and one or more volatilizable ligands. By "volatilizable" itis meant that the ligand or its component elements other than oxygen canbe removed from the substrate surface at temperatures below thecrystallization temperature of the RAC layer. In many instances organicligands breakdown to inorganic residues, such as carbonates, atrelatively low temperatures, with higher temperature being required toremove residual carbon. A ligand oxygen atom bonded directly to a metalis often retained with the metal in the RAC layer, although other ligandoxygen atoms are generally removed. At least 95 percent of the ligandsand their component atoms other than oxygen are preferably outgassed attemperatures of less than 600° C. On the other hand, to avoid loss ofmaterials before or during initial coating of the metal ligandcompounds, it is preferred that the ligands exhibit limited, if any,volatility at ambient temperatures. Metal ligand compounds having anysignificant volatility below their decomposition temperature arepreferably avoided in the practice of this invention.

Metalorganic compounds, such as metal alkyls, alkoxides, β-diketonederivatives, and metal salts of organic acids--e.g., carboxylic acids.constitute preferred metal-ligand compounds for preparing RAC precursorcoatings. The number of carbon atoms in the organic ligand can vary overa wide range, but is typically limited to less than 30 carbon atoms toavoid unnecessarily reducing the proportion of metal ions present.Carboxylate ligands are particularly advantageous in promoting metalligand solubility. While very simple organic ligands, such as oxalateand acetate ligands, can be employed in one or more metal ligandscompounds, depending upon the film forming solvent and othermetal-ligand compound choices, it is generally preferred to chooseorganic ligands containing at least 4 carbon atoms. The reason for thisis to avoid crystallization of the metal ligand compound and to improvesolubility. When heating is begun to remove the film forming solvent andligands, the solvent usually readily evaporates at temperatures wellbelow those required to remove the ligands. This results in leaving themetal-ligand compounds on the substrate surface. When the ligands havefew carbon atoms or, in some instances, linear carbon atom chains,crystallization of the metal-ligand compounds occurs. In extreme casescrystallization is observed at room temperatures. This works against themolecular level uniformity of rare earth, alkaline earth, and copperions sought by solution coating. Choosing organic ligands exhibiting 4or more carbon atoms, preferably at least 6 carbon atoms, and,preferably, ligands containing branched carbon atom chains, reducesmolecular spatial symmetries sufficiently to avoid crystallization.Optimally organic ligands contain from about 6 to 20 carbon atoms.

Instead of increasing the molecular bulk or modifying the chainconfiguration of organic ligands to avoid any propensity towardmetalorganic compound crystallization on solvent removal, anothertechnique which can be employed is to incorporate in the film formingsolvent a separate compound to act as a film promoting agent, such as ahigher molecular weight branched chain organic compound. This can, forexample, take the form of a branched chain hydrocarbon or substitutedhydrocarbon, such as a terpene having from about 10 to 30 carbon atoms.

The film forming solvents can be chosen from a wide range ofvolatilizable liquids. The primary function of the solvent is to providea liquid phase permitting molecular level intermixing of themetalorganic compounds chosen. The liquid is also chosen for its abilityto cover the substrate uniformly. Thus, an optimum film forming solventselection is in part determined by the substrate chosen. Generally moredesirable film forming properties are observed with more viscoussolvents and those which more readily wet the substrate alone, or withan incorporated wetting agent, such as a surfactant, present.

It is appreciated that a wide variety of ligands, film promoting agents,and film forming solvents are available and can be collectively presentin a virtually limitless array of composition choices.

Exemplary preferred organic ligands for metal organic compounds includemetal 2-ethylhexanoates, naphthenates, neodecanoates, butoxides,isopropoxides, rosinates (e.g., abietates), cyclohexanebutyrates, andacetylacetonates, where the metal can be any of the rare earth, alkalineearth, or copper elements to be incorporated in the RAC layer. Exemplarypreferred film promoting agents include 2-ethylhexanoic acid, rosin(e.g., abietic acid), ethyl lactate, 2-ethoxyethyl acetate, and pinene.Exemplary preferred film forming solvents include toluene,2-ethylhexanoic acid, n-butyl acetate, ethyl lactate, propanol, pinene,and mineral spirits.

As previously noted, the metal-ligand compounds are incorporated in thefilm forming solvent in the proportion desired in the final crystallineRAC layer The rare earth, alkaline earth, and copper can each be reactedwith the same ligand forming compound or with different ligand formingcompounds. The metal-ligand compounds can be incorporated in the filmforming solvent in any convenient concentration up to their saturationlimit at ambient temperature. Generally a concentration is chosen whichprovides the desired crystalline RAC layer thickness for the processsequence. Where the geometry of the substrate permits, uniformity andthickness of the metal-ligand coating can be controlled by spinning thesubstrate after coating around an axis normal to the surface of thesubstrate which has been coated. A significant advantage of spin coatingis that the thickness of the coating at the conclusion of spinning isdetermined by the contact angle and viscosity of the coating compositionand the rate and time of spinning, all of which can be preciselycontrolled. Differences in the amount of the coating composition appliedto the substrate are not reflected in the thickness of the finalcoating. Centrifugal forces generated by spinning cause excess materialto be rejected peripherally from the article.

Although processing temperatures employed in forming the amorphous RAClayers and in subsequently converting the amorphous layers tocrystalline layers can vary significantly, depending upon the specificRAC composition and crystal form under consideration, crystallization isin all instances achieved below the melting point of the RACcomposition. Melting points for RAC compositions vary, but are typicallywell above 1000° C. Typical RAC crystallization temperatures are in therange of from about 900 to 1100° C. Where crystal nucleation and growthare undertaken in separate steps, nucleation is preferably undertaken ata somewhat lower temperature than crystal growth.

In some instances X-ray diffraction has revealed the presence ofmicrocrystals in the amorphous RAC layer, although limited to minoramounts, typically less than about 5 percent, based on the total volumeof the RAC layer. While crystallization of the metal ligand compounds,which tends to separate the metals into different phases, is generallyavoided, crystallization which occurs during or immediately followingligand volatilization is not objectionable, since metals absent theirligands are free to form mixed metal oxides.

A preferred technique for producing a high T_(c) coating employing anamorphous layer of the LAC composition metal ratio I above, particularlyan LBC or LSC composition, is to heat the amorphous layer on thesubstrate to a temperature of about 925 to 975° C. to achieve crystalnucleation. Crystal growth is then undertaken at a temperature of about975 to 1050° C. Following conversion of the LAC layer to the tetragonalK₂ NiF₄ crystalline phase, it is cooled slowly at a rate of 25° C. orless per minute until it reaches a temperature of 550° to 450° C. TheLAC layer is then held at this temperature or reheated to thistemperature in the presence of an oxygen atmosphere until oxygenequilibration is substantially complete, typically about 20 to 120minutes.

A preferred technique for producing a high T_(c) coating employing anamorphous layer of the YAC composition satisfying metal ratio II above,particularly YBC, is to heat the amorphous layer on the substrate to atemperature of a temperature greater than 900° C., but less than 950°C., optimally 920° to 930° C. Following conversion of the YAC layer tothe R₁ A₂ C₃ crystalline phase, it is cooled slowly at a rate (of 25° C.or less per minute until it reaches a temperature of 750° to 400° C. TheYAC layer is then held at this temperature or reheated to thistemperature following cooling in the presence of an oxygen atmosphereuntil oxygen equilibration is substantially complete, typically about 20to 120 minutes.

From the foregoing description it is apparent that articles describedabove are comprised of a substrate and an electrically conductive layerlocated on the substrate. The electrically conductive layers iscomprised of greater than 45 percent by volume of a crystalline rareearth alkaline earth copper oxide satisfying (Ia) or (IIa)

    L.sub.2-x :M.sub.x :C:O.sub.y                              (Ia)

    Y.sub.1 :A.sub.2 :C.sub.3 :O.sub.z                         (IIa)

where

A is alkaline earth;

C is copper;

L is lanthanide;

M is alkaline earth metal;

Y is yttrium;

x is 0.05 to 0.30;

y is the amount of oxygen that results from

(a) heating an amorphous mixture of oxides of L, M and C satisfying theratio

    L.sub.2-x :M.sub.x :C                                      (I)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 925° to 975° C. to forma crystalline phase,

(b) effecting crystal growth by heating in the temperature range of from975° to 1050° C., and

(c) cooling the coating in the presence of oxygen at a rate of less than25° C. per minute until it reaches a temperature of from 550° to 450°C.; and

z is the amount of oxygen that results from

(a) heating an amorphous mixture of oxides of Y, A and C satisfying theratio

    Y.sub.1 :A.sub.2 :C.sub.3                                  (II)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 900° to 950° C. to forma crystalline phase and

(b) cooling the coating in the presence of oxygen at a rate of less than25° C. per minute until it reaches a temperature of from 750° to 400° C.

EXAMPLES

Details of the preparation and performance of articles according to thisinvention are illustrated by the following examples.

Cu(II) precursor 1

A copper precursor composition containing copper (II) 2-ethylhexanoatewas prepared by transcarboxylating 2 grams of cupric acetate with 5grams of 2-ethylhexanoic acid. The composition was heated to boiling for3 minutes to produce a total solution of 6.76 g, which was 9.4% by wt.Cu.

La precursor 1

A lanthanum precursor composition was prepared by transcarboxylating 2grams of lanthanum acetate (40.5% by wt. La) with 8 grams of2-ethylhexanoic acid to produce lanthanum 2 -ethylhexanoate.

Y precursor 1

A yttrium precursor composition was prepared by transcarboxylating 2.7grams of yttrium acetate with a stoichiometric excess (3.50 grams) of2-ethylhexanoic acid to produce yttrium 2-ethylhexanoate.

Precursor LSC-1 La₄.5 :Sr₀.5 :Cu₅

One gram of La precursor 1 was mixed with 0.0248 gram of strontium 4cyclohexanebutyrate and 0.2 gram toluene. The resulting composition washeated until the strontium compound was dissolved. Cu(II) precursor 1was then added in the amount of 0.456 gram along with 0.8 gram of rosin.The composition was adjusted to a lower viscosity by adding 0.2 gram oftoluene.

Precursor LSC-2 La₁.8 :Sr₀.2 :Cu

Two grams of La precursor 1 were mixed with 0.0499 gram of strontium 4cyclohexanebutyrate. The resulting composition was heated until thestrontium compound was dissolved. Cu(II) precursor 1 was then added inthe amount of 0.456 gram along with 1.0 gram of rosin. The compositionwas adjusted to a lower viscosity by adding 0.2 gram of toluene.

Precursor LSC-3 La₁.85 :Sr₀.15 :Cu

Two grams of La precursor 1 were mixed with 0.0364 gram of strontium 4cyclohexanebutyrate. The resulting composition was heated until thestrontium compound was dissolved. Cu(II) precursor 1 was then added inthe amount of 0.443 gram along with 1.0 gram of rosin. The compositionwas adjusted to a lower viscosity by adding 0.2 gram of toluene.

Precursor YBC-1 Y:Ba₂ :Cu₃

One half gram of Y precursor 1, 0.67 gram of Ba cyclohexanebutyrate,1.43 gram of Cu precursor 1, and 0.4 gram toluene were mixed and heatedto boiling for about 30 seconds. One gram of rosin and 0.74 grams oftoluene were then added. The composition was heated to dissolve therosin.

Precursor YBC-2 Y:Ba₃ :Cu₄

One gram of Cu precursor 1, 0.26 gram of Y precursor 1, and 0.53 gram ofbarium cyclohexane butyrate (28.86% by wt. Ba) were mixed with 1 gram oftoluene and heated to boiling for 30 seconds at which time allingredients were in solution. This was followed by the addition of 0.7gram of rosin and 0.8 gram of toluene. The composition was heated todissolve the rosin.

Precursor YBC-3 Y:Ba₄ :Cu₅

One gram of Cu precursor 1, 0.21 gram of Y precursor 1, and 0.56 gram ofbarium cyclohexane butyrate (28.86% by wt. Ba) were mixed with 1 gram oftoluene and heated to boiling for 30 seconds at which time allingredients were in solution. This was followed by the addition of 0.7gram of rosin and 0.8 gram of toluene. The composition was heated todissolve the rosin.

Example 1

This example illustrates the preparation of a high T_(c) (>30° K.)electrically conductive article prepared by forming an LSC layer on astrontium titanate substrate.

A monocrystalline strontium titanate (SrTiO₃) plate presenting a {100}upper crystal face was employed as a substrate. A small amount ofprecursor LSC-2 was placed on the substrate, which was then spun at 5000rpm for 20 seconds. A uniform, smooth coating was produced thatexhibited no physical imperfections on visual inspection, confirming thefavorable rheological properties of Precursor LSC-2 as a coatingcomposition.

The coated substrate was then heated on a hot plate to 550° C. toproduce an amorphous LSC layer. This was followed by heating to 950° C.for 5 minutes to achieve crystallization of the LSC layer and thenimmediately removed from the furnace.

The crystalline LSC layer produced exhibited a thickness of 0.3 μm andexhibited a sheet resistance of 800 ohms/sq. at a current density of 10μamperes, as measured with a four point probe at room temperature. Thisestablished the utility of the LSC layer as an electrical conductor foruse at ambient temperatures.

X-ray analysis of the layer confirmed that it exhibited a tetragonal K₂NiF₄ crystal structure. For purposes of comparing the crystallineproperties of the LSC layer with that of the corresponding bulk materiala sample of Precursor LSC-2 was placed in a crucible and heated on a hotplate to about 450° C. to produce an amorphous LSC bulk composition. Theamorphous LSC bulk composition was crystallized by heating to 900° C.for 15 minutes. X-ray diffraction analysis confirmed that both the thincrystalline layer and the bulk composition exhibited a tetragonal K₂NiF₄ crystal structure.

Sheet resistance of the crystalline LSC layer on the strontium titanatesubstrate was measured as a function of temperature as the coatedarticle was cooled to the temperature of liquid helium. Asuperconducting transition (T_(c)) was observed at approximately 40° K.,which matched that previously reported for the bulk LSC composition(note P-4 cited above). However, although sheet resistance declined fromT_(c) to about 25° K. further cooling was accompanied by increasingsheet resistance. Thus, the onset of superconductivity was observed, butsuperconductivity itself was not realized.

A plot of resistance versus temperature is shown in FIG. 4 as Curve 1.Curve 1 is plotted employing the kilo ohms scale as the ordinate.

Example 2

This example illustrates the increase of conductivity levels realizablebelow the T_(c) temperature by forming the amorphous LSC layer inmultiple process sequences.

The procedure of Example 1 was repeated, except that the layer formingprocess sequence of Example 1 prior to crystallization was performedsequentially three times. For economy of expression the resultingarticle is referred to as a 3 pass article. Although the processsequence was repeated three times, three crystalline layers were notdiscernable by microscopic inspection.

A plot of resistance versus temperature is shown in FIG. 4 as Curve 2.Curve 2 is plotted employing the ohms scale as the ordinate. While Curve2 resistance was overall much lower than that exhibited by Curve 1, thisdifference is at least partially attributable to the increased LSC layerthickness of this example. Curve 2, like Curve 1, exhibits a transitoryminimum resistance at approximately 25° K., but, unlike Curve 1, Curve 2shows a further steep drop in resistance below 25° K.

Example 3

This example is a repetition of Example 2, but with the duration ofheating to 950° C. increased from 5 minutes to 30 minutes. The resultsare plotted as Curve 3 in FIG. 4, wherein the ohms scale is employed asthe ordinate. Low temperature conductance characteristics were betweenthose of Examples 1 and Example 2, but, considering the differences inthe resistance scales, much closer to the performance characteristics ofExample 1.

This example illustrates that increasing the opportunity for substrateinteraction with the LSC layer by increasing the duration of heating tothe peak temperature for crystallization degrades low temperatureconductivity properties, but that, even with this relatively unfavorableprocess variance, the 3 pass article is still significantly superior tothe single pass article of Example 1.

Examples 4 and 5

Examples 4 and 5 were repetitions of Example 2, except that the layerforming process sequence was performed 4 and 7 times, respectively.Performance results are compared in FIG. 5, where Curve 4 represents theperformance of the 4 pass article of Example 4 and Curve 5 representsthe performance of the 7 pass article of Example 5.

These examples confirm the trend, established by comparing Examples 1and 2, that the perturbation of resistance reduction in cooling belowT_(c) can be progressively reduced by increasing the amorphous layerforming process sequence from 1 to 3 to 4 to 7 passes at 10° K. theresistance of the 7 pass article was substantially less than that of the4 pass article.

Example 6

Example 5 was repeated, but with an additional 5 minute heating to 1000°C. immediately following the step of heating for 5 minutes at 950° C.Article performance was similar to that of Example 5.

Example 7

Example 6 was repeated, but with LSC-3 substituted for LSC-2. Articleperformance was similar to that of Examples 5 and 6.

Example 8

Example 5 was repeated, but, instead of removing the article from theoven at the conclusion of heating at 950° C. for 5 minutes, the oven wasallowed to cool at the rate of 25° C. per minute. When the oven reached400° C. the article was removed. Following cooling the article wasmaintained in an oxygen atmosphere at 500° C. for 1 hour.

Sheet resistance at room temperature was lower than that observed in anyof the prior examples, being in the range of approximately 20 ohms/sq.Further, resistance declined progressively with decreasing temperatures,as is characteristic of metals. At just below 9° K. the resistance ofthe article fell below the minimum measurable resistance ofapproximately 10⁻⁵ ohm. Thus superconductivity was demonstrated. T_(c)was approximately 30° K. A slight, but discernable perturbation inresistance reduction as a function of temperature reduction wasobserved.

Example 9

Example 8 was repeated, but with an addition al 5 minute heating to1000° C. immediately following the step of heating for 5 minutes at 950°C. Further, heating in oxygen for one hour was omitted from the processsequence.

Resistance at room temperature was somewhat higher than in Example 8.FIG. 6 plots temperature versus resistance for temperatures below 100°K. T_(c) was increased to 40 to 41° K. A steeper decline in resistanceas a function of temperature reduction was observed than in any priorexample. Superconductivity was observed at 13° K. and below. An X-raydiffraction pattern of the crystalline LSC layer indicated a high degreeof crystallization in the desired tetragonal K₂ NiF₄ phase.

Example 10

Example 9 was repeated, but with the layer following cooling at acontrolled rate being held in oxygen at 500° C. for 1 hour in each layerforming process sequence.

Resistance at room temperature was reduced and resistance declinedprogressively with temperature, as is characteristic of metals,similarly as observed in Example 8 above. Resistances close to T_(c)were higher than those of Example 8, but reductions in resistance withcooling below T_(c) were similar.

Example 11

This example illustrates the preparation of a high T_(c) (>30° K.)electrically conductive artile prepared by forming a YBC layer on astrontium titanate substrate.

A monorystalline strontium titanate (SrTiO₃) plate presenting a {100}upper crystal face was employed as a substrate. A small amount ofPrecursor YBC-1 was placed on the substrate, which was then spun at 4000rpm for 20 seconds. A uniform, smooth coating was produced thatexhibited no physical imperfections on visual inspection, confirming thefavorable rheological properties of Precursor YBC 1 as a coatingcomposition. The coated substrate was then heated on a hot plate to 650°C. to produce an amorphous YBC layer. The foregoing process sequence wasperformed 7 times.

To form the final crystalline YBC layer the article was rapidly heatedto 925° C. The article was held at this temperature for 5 minutes toachieve crystallization of the YBC layer.

At the conclusion of the 5 minutes the article was allowed to coolslowly at the rate of 25° C. per minute to a temperature of 400° C. andthen removed from the firing oven. The article was then held for 1 hourat 700° C. in an oxygen atmosphere and then slowly cooled at 20° C. perminute.

The crystalline YBC layer exhibited a sheet resistance in the range of20 ohms/sq at room temperature. Resistance declined progressively withdecreasing temperature, as is characteristic of metals. FIG. 7 plotstemperature versus resistance for temperatures below 200° K. A T_(c) of85° K. was observed. Superconductivity (immeasurably low resistance) wasobserved at 53° K. and lower temperatures. No perturbation of resistanceas a function of temperature was noted below the superconductingtransition temperature.

X-ray diffraction analysis of the crystalline layer confirmed that itexhibited an R₁ A₂ C₃ crystal structure. Microscopic examinationrevealed primarily (>90% by volume of the total layer) microcrystals ofabout 2 μm in mean diameter. A second phase in the form of a fewcrystalline whiskers was also present.

Example 12

This example illustrates the preparation of a crystalline RAC layeraccording to the invention on a metal substrate.

A small amount of Precursor LSC-2 was placed on the surface of a coppersheet and formed into a smooth, uniform coating by spinning thesubstrate at 2500 rpm for 20 seconds. The resulting coated article wasthen heated to 650° C. until an amorphous LSC layer was formed. Theamorphous LSC layer was crystallized by heating to 700° C. for 2minutes.

The crystalline LSC layer produced adhered well to the copper sheetemployed as a substrate. A layer of oxide was noted to cover thesurfaces of the substrate not coated by the LSC layer. While thecrystalline LSC layer was electrically conductive, no measurableelectrical conduction between probes attached to the LSC layer andcopper sheet was observed. This suggested that an insulative layer hadbeen formed between the crystalline LSC layer and the copper sheet,probably a copper oxide.

Example 13

Example 12 was repeated, except that a 1 mil (25.4 μm) copper wire wassubstituted for the copper sheet employed as a substrate. The copperwire was coated by drawing it vertically out of a reservoir containingPrecursor LSC 2. While annular in configuration the LSC layer wasotherwise similar to that of Example 12.

This example demonstrates the ability to form crystalline RAC layers onmetal wires. The advantage of employing a wire as a substrate is thatthe resulting crystalline layer much more resilient than would bePossible if an entire article were formed of the crystalline RACcomposition.

Example 14

Example 13 was repeated, but with a glass fiber 1 mil (25.4 μm)substituted for the copper wire. A uniform coating was formed when theglass fiber was withdrawn from the precursor solution at a rate of 1mm/sec or less. The crystalline LSC layer exhibited an effective sheetresistance of 1 kilo-ohm/sq. at room temperature.

Example 15

This example demonstrates the feasibility of preparing a conductivearticle employing a YBC layer which exhibits in addition to the R₁ A₂ C₃crystalline phase a second phase.

For the purpose of comparing bulk crystalline Properties Precursor YBC 2employed as a starting material was placed in a crucible and heated on ahot plate to produce an amorphous YBC bulk composition. The amorphousYBC bulk composition was divided into two samples crystallized byheating to 925° C. for 5 and 20 minutes, respectively. X-ray diffractionanalysis showed the sample heated for 5 minutes to contain bariumcarbonate peaks, but these were absent from the sample heated for 20minutes. The latter sample exhibited an R₁ A₂ C₃ crystalline structurewith a second phase indicated by a strong peak at 29.3°.

A monocrystalline strontium titanate (SrTiO₃) plate presenting a {100}upper crystal face was employed as a substrate. A small amount ofPrecursor YBC-2 was placed on the substrate, which was then spun at 5000rpm for 20 seconds. A uniform, smooth coating was produced thatexhibited no physical imperfections on visual inspection, confirming thefavorable rheological properties of Precursor YBC-2 as a coatingcomposition. The coated substrate was then heated on a hot plate to 650°C. to produce an amorphous YBC layer. The process sequence up to thispoint was performed 7 times in sequence for each sample.

Different samples of the film were then heated to 925° C. for 5 minutesand 15 minutes, respectively, to achieve crystallization of the YBClayers. Microscopic analysis showed fewer coating defects in the 5minute sample and somewhat larger mean microcrystal grain sizes in the15 minute sample.

A third sample was then prepared as described above employingcrystallization for 5 minutes at 925° C. followed by cooling at the rateof 25° C. per minute to a temperature below 500° C. At this point theoven door was opened, allowing more rapid cooling.

At room temperature the third sample exhibited a sheet resistance of 230ohms/sq. The third sample was then heated to 700° C. rapidly in anoxygen atmosphere, held at that temperature for 1 hour, and then allowedto cool slowly. At room temperature sheet resistance was 160 ohms/sq..showing a significant reduction in sheet resistance attributable tooxygen annealing. T_(c) was observed to be 65° K.

Example 16

This example demonstrates the feasibility of preparing a conductivearticle employing a YBC layer which exhibits in addition to the R₁ A₂ C₃crystalline phase an even larger second phase than in the precedingexample.

The procedure described in Example 15 for the third sample was repeated,but with Precursor YBC-3 substituted for YBC-2. A sheet resistance of160 ohms/sq. was observed at room temperature prior to oxygen saturationand 110 ohms/sq. after oxygen saturation. Microscopic examination of theYBC layer showed a much larger proportion of second phase materialpresent, resulting in a less uniform coating.

Surprisingly, however, this example exhibited superconductivitycharacteristics superior to those exhibited by third sample of theprevious example. A plot of temperature versus resistance for the thirdsample is shown in FIG. 8. A maximum resistance was observed at 210° K.Resistance dropped rapidly with further decrease in temperature, withT_(c) =92° K. and zero resistivity being observed at temperatures of 43°K. and below.

Example 17

This example illustrates the formation of a high conductivity magnetcoil by the process of this invention.

An amorphous LSC layer was deposited on a 1102 sapphire substratefollowing the three pass amorphous LSC layer formation process describedin Example 2.

The amorphous LSC layer of the article was prepared for photoresistadhesion by being soaked for 30 seconds with hexamethyldisilazane. Thearticle was then spun at 2500 rpm for 40 seconds. Next a uniform layerof positive working photoresist (commercially available as ROKIndustries PPK3135 30.5) was applied to the amorphous LSC layer, and thearticle was again spun at 2500 rpm for 40 seconds. A smooth, uniformphotoresist layer was formed, which was dried by heating to 80° C. for20 minutes.

A mask for preparing an etched coil pattern found in conventional planarmagnets was laid on the surface of the dried photoresist. The maskformed a coiled line pattern 125 to 250 μm in width with a spacing of125 μm between adjacent line portions. The overall coil diameter wasabout 2.5 cm. Using an Oriel Corp. of America ultraviolet light source,the mask was held by vacuum deformation of a flexible diaphragm inintimate with the photoresist layer and against a transparent plate.Exposure through the transparent plate with ultraviolet radiation wasfor 12 at 17 mW/cm².

The pattern exposed photoresist was developed by being vertically dippedfor 60 seconds in developer (ROK Industries positive working photoresistdeveloper diluted 1:1 on a volume basis with deionized water). Afterdevelopment the article was rinsed with deionized water for 3 minutes.The article was then dried by heating for 2 minutes at 90° C.

The portions of the amorphous LSC layer not protected by photoresistwere then removed by etching, using a chromium etchant (commerciallyavailable as type TFD from Engelhard Industries) diluted with about 250cc of deionized water to 5 to 10 cc of etchant.

Following etching away of the unprotected LSC layer, the remainingphotoresist not exposed to ultraviolet radiation was removed by sprayingwith acetone followed by spraying with isopropyl alcohol while thearticle was being spun.

The article produced was observed to exhibit a sharp image patterncorresponding to the desired magnetic coil pattern. No visible trace ofLSC on the substrate between the convolutions of the coil was observed.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. An article comprised of a substrate and anelectrically conductive layer located on the substrate characterized inthatthe electrically conductive layer is comprised of greater than 45percent by volume of a crystalline rare earth alkaline earth copperoxide exhibiting a ratio of metals satisfying (Ia) or (IIa)

    L.sub.2-x :M.sub.x :C:O.sub.y                              (Ia)

    Y.sub.1 :A.sub.2 :C.sub.3 :O.sub.z                         (IIa)

and the substrate is comprised of alumina, where A is alkaline earth; Cis copper; L is lanthanide; M is alkaline earth; Y is yttrium; x is 0.05to 0.30; y is the amount of oxygen that results from(a) heating anamorphoux mixture of oxides of L, M and C satisfying the ratio

    L.sub.2-x :M.sub.x :C                                      (I)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 925° to 975° C. to forma crystalline phase, (b) effecting crystal growth by heating in thetemperature range of from 975° to 1050° C., and (c) cooling the coatingin the presence of oxygen at a rate of less than 25° C. per minute untilit reaches a temperature of from 550° to 450° C.; and z is the amount ofoxygen that results from(a) heating an amorphous mixture of oxides of Y,A and C satisfying the ratio

    Y.sub.1 :A.sub.2 :C.sub.3                                  (II)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 900° to 950° C. to forma crystalline phase and (b) cooling the coating in the presence ofoxygen at a rate of less than 25° C. per minute until it reaches atemperature of from 750° to 400° C.
 2. An article comprised of asubstrate and an electrically conductive layer located on the substratecharacterized in thatthe electrically conductive layer is comprised ofgreater than 45 percent by volume of a crystalline rare earth alkalineearth copper oxide exhibiting a ratio of metals satisfying (Ia) or (IIa)

    L.sub.2-x :M.sub.x :C:O.sub.y                              (Ia)

    Y.sub.1 :A.sub.2 :C.sub.3 :O.sub.z                         (IIa)

and the substrate is comprised of glass, where A is alkaline earth; C iscopper; L is lanthanide; M is alkaline earth; Y is yttrium; x is 0.05 to0.30; y is the amount of oxygen that results from(a) heating anamorphous mixture of oxides of M and C satisfying the ratio

    L.sub.2-x :M.sub.x :C                                      (I)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 925° to 975° C. to forma crystalline phase.(b) effecting crystal growth by heating in thetemperature range of from 975° to 1050° C., and (c) cooling the coatingin the presence of oxygen at a rate of less than 25° C. per minute untilit reaches a temperature of from 550° to 450° C.; and z is the amount ofoxygen that results from(a) heating an amorphous mixture of oxides of Y,A and C satisfying the ratio

    Y.sub.1 :A.sub.2 :C.sub.3                                  (II)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 900° to 950° C. to forma crystalline phase and (b) cooling the coating in the presence ofoxygen at a rate of less than 25° C. per minute until it reaches atemperature of from 750° to 400° C.
 3. An article comprised of asubstrate an dan electrically conductive layer located on the substratecharacterized in thatthe electrically conductive layer is comprised ofgreater than 45 percent by volume of a crystalline rare earth alkalineearth copper oxide exhibiting a ratio of metals satisfying (Ia) or (IIa)

    L.sub.2-x :M.sub.x :C:O.sub.y                              (I)

    Y.sub.1 :A.sub.2 :C.sub.3 :O.sub.z                         (II)

and the substrate is comprised of metal,where A is alkaline earth; C iscopper; L is lanthanide; M is alkaline earth; Y is yttrium; x is 0.05 to0.30; y is the amount of oxygen that results from(a) heating anamorphous mixture of oxides of L, M and C satisfying the ratio

    L.sub.2-x :M.sub.x :C                                      (I)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 925° to 975° C. to forma crystalline phase, (b) effecting crystal growth by heating in thetemperature range of from 975° to 1050° C., and (c) cooling the coatingin the presence of oxygen at a rate of less than 25° C. per minute untilit reaches a temperature of from 550° to 450°; and z is the amount ofoxygen that results from(a) heating an amorphous mixture of oxides of Y,A and C satisfying the ratio

    Y.sub.1 :A.sub.2 :C.sub.3                                  (II)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 900° to 950° C. to forma crystalline phase and (b) cooling the coating in the presence ofoxygen at a rate of less than 25° C. per minute until it reaches atemperature of from 750° to 400° C.
 4. An article according to claim 3further characterizes in that at least the surface of the substratecontacting the conductive layer is comprised of a refractory metal. 5.An article comprised of a substrate and an electrically conductive layerlocated on the substrate characterized in thatthe electricallyconductive layer is comprised of greater than 45 percent by volume of acrystalline rare earth alkaline earth copper oxide exhibiting a ratio ofmetals satisfying (Ia) or (IIa)

    L.sub.2-x :M.sub.x :C:O.sub.y                              (I)

    Y.sub.1 :A.sub.2 :C.sub.3 :O.sub.z                         (II)

and the substrate is comprised of an alkaline earth oxide,where A isalkaline earth; C is copper; L is lanthanide; M is alkaline earth; Y isyttrium; x is 0.05 to 0.30; y is the amount of oxygen that resultsfrom(a) heating an amorphous mixture of oxides of L, M and C satisfyingthe ratio

    L.sub.2-x :M.sub.x :C                                      (I)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 925° to 975° C. to forma crystalline phase, (b) effecting crystal growth by heating in thetemperature range of from 975° to 1050° C., and (c) cooling the coatingin the presence of oxygen at a rate of less than 25° C. per minute untilit reaches a temperature of from 550° to 450° C. and z is the amount ofoxygen that results from(a) heating an amorphous mixture of oxides of Y,A and C satisfying the ratio

    Y.sub.1 :A.sub.2 :C.sub.3                                  (II)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 900° to 950° C. to forma crystalline phase and (b) cooling the coating in the presence ofoxygen at a rate of less than 25° C. per minute until it reaches atemperature of from 750° to 400° C.
 6. An article according to claim 5further characterized in that the electrically conductive layer exhibitssuperconductivity at a temperature in excess of 10° K. and the substrateis comprised of magnesia.
 7. An article comprised of a substrate and anelectrically conductive layer located on the substrate characterized inthatthe electrically conductive layer is comprised of greater than 45percent by volume of a crystalline rare earth alkaline earth copperoxide exhibiting a ratio of metals satisfying (Ia) or (IIa)

    L.sub.2-x :M.sub.x :C:O.sub.y                              (Ia)

    Y.sub.1 :A.sub.2 :C.sub.3 :O.sub.z                         (IIa)

and the substrate exhibits a perovskite crystal structure,where A isalkaline earth; C is copper; L is lanthanide; M is alkaline earth; Y isyttrium; x is 0.05 to 0.30; y is the amount of oxygen that resultsfrom(a) heating an amorphous mixture of oxides of L, M and C satisfyingthe ratio

    L.sub.2-x :M.sub.x :C                                      (I)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 925° to 975° C. to forma crystalline phase, (b) effecting crystal growth by heating in thetemperature range of from 975° to 1050° C., and (c) cooling the coatingin the presence of oxygen at a rate of less than 25° C. per minute untilit reaches a temperature of from 550° to 450° C.; and z is the amount ofoxygen that results from(a) heating an amorphous mixture of oxides of Y,A and C satisfying the ratio

    Y.sub.1 :A.sub.2 :C.sub.3                                  (II)

in the form of a coating having a thickness of 1 μm or less on thesubstrate to a temperature in the range of from 900° to 950° C. to forma crystalline phase and (b) cooling the coating in the presence ofoxygen at a rate of less than 25° C. per minute until it reaches atemperature of from 750° to 400° C.
 8. An article according to claim 7further characterized in that the electrically conductive layer exhibitssuperconductivity at a temperature in excess of 10° K. and the substrateis comprised of strontium titanate.
 9. An article according to claim 7further characterized in that the metal is copper.
 10. An articleaccording to any one of claims 1, 5, 6, 7, 8, 2, 3, 9 and 4 furthercharacterized in that the conductive layer is restricted to a portion ofthe substrate thereby defining a conduction path on the substrate. 11.An article according to claim 2, 9 or 3 further characterized in thatthe substrate is of an elongated configuration and the conductive layerforms a conductive sheath surrounding the substrate.
 12. An articleaccording to claim 11 further characterized in that both the substrateand the conductive layer are flexible.
 13. An article according to claim12 further characterized in that the conductive layer has a thickness of2 μm or less.
 14. An article according to any one of claims 1, 5, 6, 7and 8 further characterized in that the substrate is monocrystalline.15. An article according to any one of claims 1, 6, 7, 8, 2, 3, or 9further characterized in that a barrier is interposed between thesubstrate and the electrically conductive layer.
 16. An electricallyconductive article according to any one of claims 5, 6, 7, or 8 furthercharacterized in that the conductive layer exhibits a superconductingtransition temperature of at least 30° K.
 17. An article according toclaim 16 further characterized in that the conductive layer exhibits asuperconducting transition temperature of at least 80° K. and iscomprised of an R₁ A₂ C₃ crystalline phase.
 18. An article according toany one of claims 1, 5, 6, 7, 8, 2, 3, 9 or 4 further characterized inthat the conductive layer consists of greater than 70 percent by volumeof a crystalline conductive phase.
 19. An article according to claim 18further characterized in that the conductive layer consists of greaterthan 90 percent by volume of a crystalline conductive phase.
 20. Anarticle according to any one of claims 1, 5, 6, 7, 8, 2, 3, and 4further characterized in that greater than 45 percent by volume of theconductive layer consists essentially of a rare earth alkaline earthcopper oxide which is in an tetragonal K₂ NiF₄ crystalline form.
 21. Anarticle according to claim 20 further characterized in that the rareearth alkaline earth copper oxide satisfies the metal ratio:

    L.sub.2-x :M.sub.x :Cu

where L is lanthanide, M is alkaline earth metal, and x is 0.05 to 0.30.22. An article according to claim 18 further characterized in thatgreater than 70 percent by volume of the conductive layer consistsessentially of a rare earth alkaline earth copper oxide which satisfiesthe metal ratio

    L.sub.2-x :M.sub.x :Cu

where L is lanthanide, M is alkaline earth metal, and x is 0.050 to0.30.
 23. An article according to claim 22 further characterized in thatthe lanthanide is lanthanum and the alkaline earth metal is barium orstrontium.
 24. An article according to claim 22 further characterized inthat x is 0.15 to 0.20.
 25. An article according to any one of claims 1,5, 6, 7, 8, 2, 3, 9 and 4 further characterized in that greater than 45percent by volume of the conductive layer consists essentially of a rareearth alkaline earth copper oxide which is in an R₁ A₂ C₃ crystallinephase.
 26. An article according to claim 25 further characterized inthat the rare earth alkaline earth copper oxide consists of yttrium asthe rare earth and barium, optionally in combination with at least oneof strontium and calcium, as the alkaline earth.
 27. A superconductivearticle comprised of a substrate and a superconductive layer located onthe substrate, characterized in thatthe layer exhibits superconductivityat a temperature in excess of 10° K. and consists of greater than 45percent by volume of a crystalline tetragonal K₂ NiF₄ phase consistingessentially of a rare earth alkaline earth copper oxide satisfying (Ia):

    L.sub.2-x :M.sub.x :Cu:O.sub.y

where L is lanthanum, M is strontium, and x is 0.050 to 0.30, y is theamount of oxygen which results from(a) forming an amorphous oxidecoating having a thickness of less than 1 μm by (i) preparing a solutioncomprised of a volatile film-forming solvent and metalcarboxylate ligandcompounds of the lanthanum, strontium and copper in the mole ratio (I)

    L.sub.2-x :M.sub.x :C                                      (I)

where L, M, C and x are as indicated above, (ii) coating the solution onthe substrate, and (iii) removing the solvent and ligands from thesubstrate by heating in the presence of oxygen, (b) heating theamorphous oxide to a temperature in the range of from 925° to 975° C. toform a crystalline phase, (c) effecting crystal growth by heating in thetemperature range of from 975° to 1050° C., and (d) cooling the coatingin the presence of oxygen at a rate of less than 25° C. per minute untilit reaches a temperature of from 550° to 450° C.; and the substrateconsists essentially of monocrystalline strontium titanate.
 28. Asuperconductive article according to claim 27 further characterized inthat x is 0.15 to 0.20.
 29. A superconductive article according to claim27 further characterized in that the layer exhibiting superconductivityconsists of greater than 90 percent by volume of the crystalline phase.30. A superconductive article comprised of a substrate and asuperconductive layer located on the substrate, characterized in thatthelayer exhibits superconductivity at a temperature in excess of 30° K.and consists of greater than 45 percent by volume of an R₁ A₂ C₃crystalline phase which consists essentially of a rear earth alkalineearth copper oxide, the rare earth alkaline earth copper oxide consistsof yttrium as the rare earth and barium, optionally in combination withstrontium as the alkaline earth, the yttrium, alkaline earth, and copperare present in a 1:2:3 mole ratio n the R₁ A₂ C₃ phase, the amount ofoxygen in the R₁ A₂ C₃ phase is that which results from(a) forming anamorphous oxide coating having a thickness of less than 1 μm by (i)preparing solution comprised of a volatile film-forming solvent andmetal-carboxylate ligand compounds of the yttrium, alkaline earth andcopper in the 1:2:3 mole ratio, (ii) coating the solution on thesubstrate, and (iii) removing the solvent and ligands from the substrateby heating in the presence of oxygen, (b) heating the amorphous oxidecoating to a temperature in the range of from 900° to 950° C. to form acrystalline phase and (c) cooling the coating in the presence of oxygenat a rate of less than 25° C. per minute until it reaches a temperatureof from 750° to 400° C., and the substrate consists of monocrystallinemagnesia or strontium titanate.
 31. A superconductive article accordingto claim 30 further characterized in that the layer exhibitingsuperconductivity consists of greater than 90 percent by volume of thecrystalline phase.
 32. A superconductive article according to claim 30further characterized in that the substrate consists essentially ofmagnesia.
 33. A superconductive article according to claim 30 furthercharacterized in that the substrate consists essentially of strontiumtitanate.
 34. An article comprised of a substrate and a layer of anamorphous metal oxide located on the substrate characterized in thattheamorphous metal oxide is a rare earth alkaline earth copper oxidecapable of being converted to an electrically conductive crystallineform accounting for at least 45 percent by volume of the layer, thesubstrate is comprised of alumina, the oxide exhibits a ratio of metalssatisfying (I) or (II)

    L.sub.2-x :M.sub.x :C                                      (I)

    R.sub.1 :A.sub.2 :C.sub.3                                  (II)

where A is alkaline earth; C is copper; L is lanthanide; M is alkalineearth; R is rare earth; and x is 0.05 to 0.30, andthe oxygen content ofthe amorphous oxide coating is that which results from (i) forming asolution comprised of a volatilizable film-forming solvent andmetalcarboxylate ligand compounds of the metals and in the proportionsof (I) or (II), (ii) coating the solution on the substrate, and (iii)removing the solvent and ligands from the substrate by heating in thepresence of oxygen.
 35. An article according to claims 34 and inclusivefurther characterized in that the substrate presents a planar surfaceand the amorphous metal oxide forms a planar layer on the planarsubstrate surface.
 36. An article according to claim 34 and inclusivefurther characterized in that a removable protective layer overlies theamorphous layer.
 37. An article comprised of a substrate and a layer ofan amorphous metal oxide located on the substrate characterized inthatthe amorphous metal oxide is a rare earth alkaline earth copperoxide capable of being converted to an electrically conductivecrystalline form accounting for at least 45 percent by volume of thelayer, the substrate is comprised of an alkaline earth oxide, the oxideexhibits a ratio of metals satisfying (I) or (II)

    L.sub.2-x :M.sub.x :C                                      (I)

    R.sub.1 :A.sub.2 :C.sub.3                                  (II)

where A is alkaline earth; C is copper; L is lanthanide; M is alkalineearth; R is rare earth; and x is 0.05 to 0.30, andthe oxygen content ofthe amorphous oxide coating is that which results from (i) forming asolution comprised of a volatilizable film-forming solvent andmetalcarboxylate ligand compounds of the metals and in the proportionsof (I) or (II), (ii) coating the solution on the substrate, and (iii)removing the solvent and ligands from the substrate by heating in thepresence of oxygen.
 38. An article according to claim 31 furthercharacterized in that the substrate is magnesia.
 39. An articlecomprised of a substrate and a layer of an amorphous metal oxide locatedon the substrate characterized in thatthe amorphous metal oxide is arear earth alkaline earth copper oxide capable of being converted to anelectrically conductive crystalline form accounting for at least 45percent by volume of the layer, the substrate is exhibits a perovskitecrystal structure, the oxide exhibits a ratio of metals satisfying (I)or (II)

    L.sub.2-x :M.sub.x :C                                      (I)

    R.sub.1 :A.sub.2 :C.sub.3                                  (II)

where A is alkaline earth; C is copper; L is lanthanide; M is alkalineearth; R is rare earth; and x is 0.05 to 0.30, andthe oxygen content ofthe amorphous oxide coating is that which results from (i) forming asolution comprised of a volatilizable film-forming solvent andmetalcarboxylate ligand compounds of the metals and in the proportionsof (I) or (II), (ii) coating the solution on the substrate, and (iii)removing the solvent and ligands from the substrate by heating in thepresence of oxygen.
 40. An article according to claim 39 furthercharacterized in that the substrate is comprised of strontium titanate.41. An article comprised of a substrate and a layer of an amorphousmetal oxide located on the substrate characterized in thatthe amorphousmetal oxide is a rare earth alkaline earth copper oxide capable of beingconverted to an electrically conductive crystalline form accounting forat least 45 percent by volume of the layer, the substrate is comprisedof glass, the oxide exhibits a ratio of metals satisfying (I) or (II)where A is alkaline earth; C is copper; L is lanthanide; M is alkalineearth; R is rare earth; and x is 0.05 to 0.30, andthe oxygen content ofthe amorphous oxide coating is that which results from (i) forming asolution comprised of a volatilizable film-forming solvent andmetalcarboxylate ligand compounds of the metals and in the proportionsof (I) or (II), (ii) coating the solution on the substrate, and (iii)removing the solvent and ligands from the substrate by heating in thepresence of oxygen.
 42. An article comprised of a substrate and a layerof an amorphous metal oxide located on the substrate characterized inthatthe amorphous metal oxide is a rare earth alkaline earth copperoxide capable of being converted to an electrically conductivecrystalline form accounting for at least 45 percent by volume of thelayer, the substrate is comprised of metal, the oxide exhibits a ratioof metals satisfying (I) or (II)

    L.sub.2-x :M.sub.x :C                                      (I)

    R.sub.1 :A.sub.2 :C.sub.2                                  (II)

where A is alkaline earth; C is copper; L is lanthanide; M is alkalineearth; R is rare earth; and x is 0.05 to 0.30, andthe oxygen content ofthe amorphous oxide coating is that which results from (i) forming asolution comprised of a volatilizable film-forming solvent andmetalcarboxylate ligand compounds of the metals and in the proportionsof (I) or (II), (ii) coating the solution on the substrate, and (iii)removing the solvent and ligands from the substrate by heating in thepresence of oxygen.
 43. An article according to claim 42 furthercharacterized in that the metal forming the substrate is comprised ofcopper.
 44. An article according to any one of cl aims 1, 10, 14, 6 or7, further characterized in thatA is barium optionally in combinationwith at least one of strontium and calcium.
 45. An article according toany one of claims 1, 10, 14, 6 or 7, further characterized in thatL islanthanum.
 46. An article according to any one of claims 1, 10, 14, 6 or7, further characterized in thatM is at least one of barium andstrontium.
 47. An article according to any one of claims 1, 10, 14, 6 or7, further characterized in thatA is barium optionally in combinationwith at least one of strontium and calcium; L is lanthanum and M is atleast one of barium and strontium.